661091979700681 has 9 divisors (see below), whose sum is σ = 661794474364149. Its totient is φ = 660390230026944.

The previous prime is 661091979700679. The next prime is 661091979700759. The reversal of 661091979700681 is 186007979190166.

The square root of 661091979700681 is 25711709.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 257862286564281 + 403229693136400 = 16058091^2 + 20080580^2 .

It is not a de Polignac number, because 661091979700681 - 2¹ = 661091979700679 is a prime.

It is a super-2 number, since 2×661091979700681² (a number of 30 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 661091979700681.

It is not an unprimeable number, because it can be changed into a prime (661091979700601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 25120326535 + ... + 25120352851.

Almost surely, 2^{661091979700681} is an apocalyptic number.

661091979700681 is the 25711709-th square number.

661091979700681 is the 12855855-th centered octagonal number.

It is an amenable number.

661091979700681 is a deficient number, since it is larger than the sum of its proper divisors (702494663468).

661091979700681 is an frugal number, since it uses more digits than its factorization.

661091979700681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54588 (or 27294 counting only the distinct ones).

The product of its (nonzero) digits is 61725888, while the sum is 70.

The spelling of 661091979700681 in words is "six hundred sixty-one trillion, ninety-one billion, nine hundred seventy-nine million, seven hundred thousand, six hundred eighty-one".